The purpose of the testing of unvulcanized rubber is for the better assessment and control of its behaviour during manufacturing processes such as calendering and extrusion.
The machine used at present for such testing is the Mooney Rheometer. It is a standard machine in the industry in spite of the fact that it has been recognized for some considerable time that it has deficiencies most notably that it works at a low shear rate, approximately 1 reciprocal second, whereas during extrusion of the rubber is subjected to a shear in the region of 100 sec.sup.-1 and during injection moulding 1000 sec.sup.-1. It is inherent in the Mooney machine that it cannot be efficiently operated at high shear rates.
The sample to be tested is placed in the rotor chamber and a closure is applied to the chamber. Usually excess material is placed in so that when the two halves of the chamber are closed together the excess has to escape between the lands of the two halves. Not only does this eventually cause wear and loss in precision in the chamber as well as uncertainty as to the precise size of the chamber but this also means that no ascertainable pressure is exerted or maintained on materials in the chamber.
A machine working on the principle of the Mooney can only be used to measure viscosity. In some processes, especially extrusion, the elasticity of the rubber has a pronounced effect on the product and this shows that a test instrument is needed which operates at higher shear rates and which will also convey information on the elastic properties of the rubber being tested. Within the invention this is done not only by providing a test machine but also a test method operable by means of that machine which reveals knowledge about other characteristics of the rubber.